A vehicle is mounted with a TCU and a vehicular modem. The TCU may provide various communication functions and host function by being connected to the vehicular modem. For example, the TCU can provide, by being connected to the vehicular modem, e-call, completely automated accident warning, defect call, local-support service telephone, traffic information, remote control lock, vehicle finding, remote-control diagnosis and vehicle data. The TCU can also perform the function of data modem to other devices mounted in a vehicle. The TCU may manage phone calls, and perform various call functions such as multi-phone hook-up and phone book data restoration. The TCU may automatically transmit a vehicle position in an accident or an emergency situation, and connect a voice phone.
Meantime, a vehicular modem maintains a service-on state by periodically monitoring a communication environment for a stable communication service. In addition, the TCU may maintain a modem in a standby state in order to start a vehicle or to receive a signal from a user for a predetermined time. For example, the modem may be set to maintain a standby state for 96 hours.
However, when a vehicle enters a communication shadow area or a vehicle is parked, the modem may be in a no-service state by deviating from the service on-state. Thus, in this case, a current consumption in modem disadvantageously increases to thereby result in a battery discharge in the vehicle, because many attempts are being made to secure communication channels.